1. Field of the Invention
This invention relates to the field of orthodontics and more particularly to a system and method for detecting deviations from a planned course of treatment to gradually reposition teeth.
2. Background
A fundamental objective in orthodontics is to realign or reposition a patient's teeth to positions where the teeth function optimally and aesthetically. Methods have been developed to reposition a patient's teeth to a prescribed tooth arrangement (i.e. a desired final arrangement of each tooth in a patient's jaw) according to a planned course of treatment using a series of appliances. The series of incremental position adjustment appliances are placed over the patient's teeth and gradually reposition the teeth. Each appliance represents a pre-existing stage in a series of pre-existing stages for repositioning teeth to a prescribed final position. This is described in U.S. Pat. No. 5,975,893; which is assigned to the assignee of the present application, and the complete disclosures of which is incorporated herein by reference.
Ideally, a patient wears each appliance for about two weeks or until the pressure of each appliance on the teeth can no longer be felt. At that point, the patient replaces a current adjustment appliance with a next adjustment appliance in the series until no more appliances remain. During treatment, a patient may forget to wear the appliances regularly allowing the patient to stray from the prescribed course. As a result, one or more appliances may not properly fit and the dentist (or any other medical professional) may have to start the process again (“re-start”) by taking another impression of the patient's teeth so that a new series of incremental position adjustment appliances can be electronically generated and ultimately manufactured to a new prescribed tooth arrangement.
When a re-start occurs, there is an opportunity to track what progress has occurred to straighten the patient's teeth. To accurately track the progress of a patient's teeth, it is desirable to have an exact model of the patient's teeth for comparison.
Conventional methods provide process steps for creating generalized record keeping for images of a patient's teeth by moving standard teeth in a standard three-dimensional (3D) digital model template to reflect the general position of a patient's teeth. Since the size and shape of any tooth of the standard 3D model may vary from actual teeth of the patient, the images may only provide a visual likeness and not an exact tooth structure or position to allow for accurate tracking of tooth movement or fabrication of adjustment appliances, such as aligners, which use actual teeth geometry.
In conventional methods, a patient's X-ray image is displayed on a computer screen as a background image for the standard 3D model. The standard 3D model is then rotated, translated and scaled by a technician to match the orientation of the X-ray image. Then the individual teeth are adjusted to match those in the X-ray. However, the model generated by conventional methods is not an exact model of the patient's teeth but merely an approximate model of the patient's teeth because instead of actual patient teeth, standard teeth are used. Hence, the patient's progress cannot be accurately tracked and reliable data is unavailable to manufacture adjustment appliances.
Therefore, a system and method for detecting deviations from a prescribed course of treatment to gradually reposition teeth to a pre-existing prescribed tooth arrangement; and accurately tracking the progress of a patient's teeth are needed.